Assuming you're talking about USA usage, you're correct, a "cup" is usually 6oz. In the USA, the standard size for a "cup" of coffee is 6oz, even though nobody drinks cups of coffee that small (12oz to 20oz is more common). For that matter, the size of a "cup" of tea can be 5oz or 6oz when the number of "cups" a teapot holds is listed; a "6 cup" teapot is only 32oz.
However, be careful how the word is used in American recipes. If a recipe calls for a "cup" of coffee, they are more likely to be calling for an 8oz cup, rather than a 6oz cup.
I can't find a clear reference as to where the unrealistic 6oz measurement for a cup of coffee started. Possibly the result of Mr. Coffee, but we're stuck with it as customary now.
However, even though a 6oz cup of coffee may be customary, specific coffee maker manufacturers may use different measurements on different models, including cups as small as 4.2oz. So don't assume unless you've checked.
Oh, and also note that the 8oz cup is American, rather than Imperial measurement. An Imperial cup is around 10oz, although you're unlikely to encounter this measurement in any recipe published after World War I.
Confused yet?
Ask them for Brennspiritus. You can get it in bigger drugstores like DM or Rossmann, I don't know who else will have it, but maybe home maintenance (?) stores (Baumärkte).
You can't use butane, that's a different fuel and obviously not suitable for your case. You should be able to use pure ethanol, but due to alcohol import laws, medicinal ethanol without dilutants is extremely expensive, and medicinal ethanol with dilutants might have dilutants which create something bad when burned. Brennspiritus is ethanol with dilutants which can be burned safely, while still making it undrinkable.
If everything else fails, you can start burning high-percentage drinking alcohol, my grandpa uses it sometimes on Spiritus burners. The problem (besides being more expensive) is that you need both a high ABV (something around 70% will be good) and a pure alcohol (vodka or obstwasser); alcohol types which you are likely to find at these percentages (such as rum) can leave layers of badly combusted gunk inside the burner.
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This is actually the Turkish method for making coffee, or a variant of it. Coffee grounds, cold water and sugar are brought just to a boil several times before being poured into small cups. For this method one typically uses the finest possible grind of coffee.
The sand is used to control heat. The pots (called cezve) on top of the sand keep warm, and when you want them to boil you push them down through the sand to make direct contact with the hot plate underneath.